1. Field of the Invention
The present invention relates to a fast Duplicate Address Detection (DAD) Entity for managing information for fast DAD performance in the distribution system and a method for carrying out DAD efficiently using the fast DAD Entity, and more particularly, to a structure of the fast DAD Entity for managing mobile node address information for fast DAD performance in the distribution system using the Inter-Access Point Protocol (IAPP) and a method using the fast DAD Entity for shortening the DAD time it takes to assign a Care-of Address (CoA) to a mobile node.
2. Description of the Related Art
Recently, the number of wireless internet users has increased along with the rapid development of internet supplies. There have also been more wireless communications technology developments, and improved performance of mobile terminals such as portable computers, Personal Digital Assistants (PDAs), and so on. Under the wireless internet environment, a mobile terminal frequently roams around to change its own network point of attachment. Such a mobile terminal is referred to as a mobile node.
According to the mobile IPv6, a mobile node communicates with a Correspondent Node (CN) using its own home address through its Home Agent (HA) which is a router having its own registration information, even in the event that the mobile node roams to a Foreign Network. If a mobile node is linked to a foreign network, the mobile node is assigned a temporary address, that is, a CoA, from the foreign network, and performs registration, that is, sends binding update messages to its Home Agent together with its home address.
A mobile node joins the Solicited-node Multicast Address in its linked foreign network, randomly generates a new CoA that it attempts to use, and multicasts to its newly linked network, Neighbor Solicitation messages including its own IP address, Link-Layer address, generated CoA, and so on, to have the DAD carried out.
If the mobile node fails to receive a Neighbor Advertisement message notifying of address duplication within a predetermined limited time RetransTimer, the new CoA is recognized as a unique CoA, and the mobile node performs communications using the new CoA. The predetermined limited time RetransTimer is 1000 ms by default.
However, if a node attached to the sub-network is using the new CoA, the node sends to the mobile node, Neighbor Advertisement messages including its own Link-Layer address in a reply to the Neighbor Solicitation messages. Thus, the mobile node re-generates its interface identifier (ID) at random, re-generates a new CoA, and has the DAD procedure performed again for the newly generated CoA.
As stated above, according to the existing mobile IPv6, a wait time as much as the default time of RetransTimer is required, even in the event that the DAD succeeds. Therefore, the mobile node cannot use the CoA set as a temporary address for the waiting time, which causes a considerable packet loss when in handoff mode.
There exists the Optimistic DAD (ODAD) as a scheme proposed to solve the above problem. The ODAD is based on the assumption that the DAD is far more likely to succeed than to fail. Accordingly, a mobile node immediately uses a generated new CoA (NCoA) as a temporary address and performs communications without waiting till the DAD succeeds.
However, when an address is duplicated, the ODAD causes troubles to the mobile node that uses the address as a new address as well as to another mobile node that has configured the same address previously. That is, in the event that the mobile node that uses the address as a new address attempts to send packets or receive packets from a Correspondent Node, the mobile node may be disconnected with the Correspondent Node since packets can be delivered to the mobile node that has configured the same address previously. Further, the ODAD has a problem in that the introduction to the concept of temporary address before DAD adds complexity to the IPv6 configuration.